Recently, 3C electronic devices such as notebook computers, folding cell phones, digital cameras and the like are developed to be lighter, thinner, shorter and smaller, which has become the trend of development of electronic technique and communication devices and further increased the demand for a “secondary battery” as a portable power supply. Accordingly, secondary batteries have been also developed to be thinner, smaller and lighter. Meanwhile, the requirement of capacitance of a secondary battery is increased in response to the need of electronic devices with multifunction, high speed, high performance and high power.
Generally, a lithium ion battery has an energy density about 260 to 270 kWh/m3, which is about 2 folds or higher of the energy density of a nickel-cadmium alkaline secondary battery. Lithium ion/lithium-polymer secondary batteries have the advantages such as rapid charging rate, high discharging power and high energy density, so that lithium ion batteries and lithium-polymer batteries have played important roles in the application of small-scaled electronic devices among all secondary batteries. However, there still is a need to focus on safety, capacitance and cycle life at high temperature and high pressure for batteries in battery industry and electric vehicles.